A fair question. In principle this can happen, and HotSpot can respond to changes in the program's execution patterns, but to my knowledge it's not a problem in practice with real-world Java servers. Other than a 'warming up' phase, real-world performance doesn't tend to vary wildly as time progresses.
(Disclaimer: I've not done a great deal of real-world Java work.)
(Disclaimer: I've not done a great deal of real-world Java work.)